Ireland's "real aim" in Brexit negotiations is to force the UK to stay within the EU's customs union, according to the DUP's deputy leader.

Nigel Dodds, who leads the Northern Ireland party at Westminster, hit out at Ireland's stance over the UK's exit talks as he accused Dublin of a "rigidity" regarding Irish border issues.

Ireland has recently demanded a formal written guarantee that there will be no hard border with Northern Ireland before it will sanction Brexit negotiations moving on to their next phase, on future EU-UK trade arrangements.

But, calling for "flexible and imaginative" solutions from Brussels and Dublin, Mr Dodds claimed Ireland has dismissed the UK's own proposals to avoid such a scenario.

"Their real aim is to try to get to a situation where either they try to force the UK as a whole to stay within the customs union, which is in their interests, clearly," Mr Dodds told Sky News.

"Or, if they fail that, to at least force Northern Ireland to stay within the customs union and the single market, follow the rules of it, something then we'd have no say over, but we'd have to abide by the rules, which would then bring about a united Ireland much easier."

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Video:A way to solve the Irish border question?

Mr Dodds highlighted a UK Government position paper on the Irish border, published earlier this year, which suggested there will no need for post-Brexit customs checks on the island of Ireland due to exemptions and trusted trader schemes.

The DUP politician added it would be "economic madness" and "politically unacceptable" for Northern Ireland to be separated from the rest of the UK by remaining in the customs union or single market.

Theresa May has insisted the whole of the UK will be leaving both the customs union and single market after Brexit.

Downing Street was forced to clarify this position remains the same on Friday, after a spokesman had earlier told a Westminster briefing Northern Ireland's continuing membership of the customs union was "a matter for negotiation".

Meanwhile, there were further signals the Irish border issue has become a major sticking point before a crunch EU summit next month, when the Prime Minister hopes European leaders will sanction the start of phase two Brexit talks.

Speaking at a separate Brussels summit with eastern European nations on Friday, Ireland's foreign minister Simon Coveney said it was difficult to see how border checks could be avoided if Brexit resulted in "regulatory divergence" between the UK and EU.

"We can't move to phase two on the basis of aspiration," he said.

"We have move to phase two on the basis of a credible road map or the parameters around which we can design a credible road map to ensure that it doesn't happen."